Nearly 10 percent of all patients with BPD commit suicide and up to 75 percent make at least one suicide attempt. While many of these attempts are low in medical lethality, 50 percent of individuals with BPD have made at least one suicide attempt that is highly lethal. Despite this severity, the frequency of low lethality suicide attempts and non-suicidal self-injury in BPD leads clinicians to consider suicide attempts as merely "gestures," or manipulative and attention-seeking behaviors. Also, clinicians tend to treat suicidality in BPD by treating the symptoms of depression, when, in fact, impulsivity appears to be a stronger risk factor. We will examine clinical and neurobiological factors related to suicide attempts in subjects with borderline personality disorder using a prospective design. Through the administration of structured clinical interviews and lumbar puncture, we plan to measure various state and trait variables that pose risk for suicidal behavior in a cohort of 300 subjects: 200 with BPD (100 attempters, 100 non-attempters) between the ages of 18-35, the period of highest suicide risk in BPD and 100 attempters with Major Depression without an Axis II diagnosis. The specific aims are to: 1. examine clinical state and trait predictors of suicide attempts during a two year follow-up; and 2. examine serotinergic function (e.g., CSF-5HIAA) and other biological indices of suicide attempt behavior in BPD during a two year follow-up. Exploratory aims include: 1. identify the risk factors for high lethality versus low lethality attempts in BPD; 2. determine co-morbidity of Major Depression at time of attempts; 3. apply a stress-diathesis model to examine the interaction of state and trait factors in determining risk for suicidal behavior in BPD; 4. explore the relationship of self-mutilation and dissociation with suicidal acts, and with state and trait risk factors. The difficulty in predicting suicidal behavior in the treatment of BPD leads to either under-recognition of the seriousness of suicidal risk in BPD, or alternatively, over-utilization of hospitalization. These findings may have important clinical application for more accurate prediction of high lethality attempts within the context of frequent low lethality suicidal behaviors.